Hormesis and ecological risk assessment: Fact or fantasy?

Hormesis is a widespread phenomenon across occurring many taxa and chemical s, and, at the single species level, issues regarding the application of ho rmesis to human health and ecological risk assessment are similar. However, interpreting the significance of hormesis for even a single species in an ecological risk assessment can be complicated by competition with other spe cies, predation effects, etc. In addition, ecological risk assessments may involve communities of hundreds or thousands of species as well as a range of ecological processes. Applying hermetic adjustments to threshold effect levels for chemicals derived from sensitivity distributions for a large num ber of species is impractical. For ecological risks, chemical stressors are frequently of lessor concern than physical stressors (e.g., habitat altera tion) or biological stressors (e.g., introduced species), but the relevance of hormesis to non chemical stressors is unclear. Although ecological theo ries such as the intermediate disturbance hypothesis offer some intriguing similarities between chemical hormesis and hermetic-like responses resultin g from physical disturbances, mechanistic explanations are lacking. While f urther exploration of the relevance of hormesis to ecological risk assessme nt is desirable, it is unlikely that hormesis is a critical factor in most ecological risk assessments, given the magnitude of other uncertainties inh erent in the process.